Heat treatment of magnesium base alloys



March 23, 1943. A. BRANDT' 2,314,354

HEAT TREATMENT OF MAGNESIUM BASE ALLOYS Original Filed Oct. 8, 1941 0.1 /0 fi e/d Paiaf fans w a P Alloy Patented Mar. 23, 1943 r nm'r TREATMENT or MAGNESIUM aasaamors Alfred Brandt, Swansea, Wales, assignor, by mesne assignments, to The Anglo California National Bank or San Franciscqsan Francisco, Calif, a national banking association, as trustee Original application October a. .1941. Serial is. 414,178. Divided and this application. Au st 5, 1942, Serial No. 453,131. In Great 111mm September 9, 1940 ZCIaims. (01. 148-213) This'invention relates to high percentage magnesiumbase alloys and is particularly concerned with raising the yield point (proof stress) of the alloys by subjecting the same in the "as-cast" condition to a single-step heat treatment within a range of not less than 100 C. but less than 250 C., having avoided any previous thermal treatment at higher temperatures.

It is an object of th present invention to avoid the so-called solution heat treatment at temperatures far above 250", which constitutes, with subsequent chilling, the first stage of the thermal treatment of magnesium base alloys which has theretofore been the standard practice in treating castings of this type, an annealing treatment at a lower temperature, below 200 6., being PM erably carried out as a second stage. The singlestep thermal treatment at low temperature leaves the strength of thematerial substantially unaltered, and the elongation may even decrease to some extent. On the other hand, the yield point is materially increased. Uniformity 0! results, reduction of wastage, the lessening of fire risks, are also possible advantages.

According to the present invention, the singlestep heat treatment between 100 C. and 250 C. is applied to magnesium base alloys containing more than 7% but less that-12% of aluminum, and also containing from 0.1% to 1.0% of manganese, the total amount oi-alloying constitutents being not above 12%.

The following examples illustrate various instances which are according to the present invention, the percentages being by weight and subject to tolerances for usual impurities.

The drawing shows the results of tests with various magnesium base alloy castings indicatin both the yield point, intons per square inch, for 0.1% permanent deformation in the alloy in the cast and non-heat treated condition and in re spect oi the cast alloy heat treated to give what appear to be optimum results, the absci'ssae being arranged in order of decreasing amounts or total alloying constituents and ordinates corresponding to yield point in tons per square inch.

Turning now to Figure 1 and reading from the left, the eflect or the heat treatment or magnesium base allow castings A to C inclusive of the square inch of the heat-treated casting, the line.

in the same column somewhat below it indicating the yield point or the unheat-treated alloy, that is to say, the alloy in the condition resulting from casting, or in other words, the condition known as "as cast" condition.

The table given below contains the percentages by weight of the casting subject to tolerance for usual impurities together with the heat treatment which they received, namely:

as Al Mn Total mentin days at a 11.28 0.31 11.50 31175 B 10.39 0.0a 11.05 3x140 o 6.67 0.3a 0.90 11175 In preparing the above examples and diagrams. alloys were made up and cast into tensile test bars in accordance with the specifications oi the British Air Ministry Department of Technical Development. Yield point, in tons per square inch, for 0.1% permanent eloniation was determined in the case of each alloy in the as cast condition, and after heat treatment at C. for 1, 2 and 3 days, after heat treatment at C. for l, 2 and 3 days, after heat treatment at 240 alloying constituents being not above 12% the balance being substantially all magnesium, which comprises subjecting such alloys in the as-cast" condition to a heat treatment at a temperature within the range'oi 100 C. to 250 C.

2. An alloy consisting principally of magnesium and containing from '1 to 12% of aluminum and from 0.1% to 1.0% of manganese, and the balance substantially all magnesium, the total amount or alloying-constituents not exceeding 12%, in the form oi shaped castings the yield point of which has been raised without appreciable increase in strength by heat treatment in the as-cast" condition at a temperature within the range of 100' C. to 250 C.

AIJ'RED BRANDT. 

